I currently have a post about how there are four bosses in the game that utterly ignore Hydraulic Overrides (since the tooltip does say that it makes you immune to physics such as knockbacks - and in my opinion grapples also fall under physics). The Savrip boss in H2+ The Specialists ignores the hydraulic overrides, as does General Ortol, Darth Malgus and Jindo Krey. They all ignore the Hydraulic Overrides. It's most troublesome against General Ortol in Cademimu because he'll knock you into the rocket flames even if you have Hydraulic Overrides going. If you're beside him or slightly behind him, he WILL turn and slap you into the rocket exhaust and kill you. Nobody has yet to give me a valid reason why these four bosses will ignore the Hydraulic Overrides which the tooltip says makes you immune to physics for 10 seconds (Advanced Prototype Powertech talent). It should be pointed out that those four are Bosses. With a Boss buff. There is the Temple Guardian in Athiss that also ignores Hydraulic Overrides. They aren't bosses, they're standard champions.
Jindo Krey will yank you from the panel if you have Hydraulic Overrides going. He won't try to yank you UNTIL you touch the panel, and I have tested it numerous times with Hydraulic Overrides running and him yanking me from the panel. And this is right after I activate them and touch the panel. So yes, I was under the influence of Hydraulic Overrides before he pulled me. I haven't tried this with a smuggler or sniper, but if the Hunker Down/Entrench works perfectly against him, why doesn't Hydraulic Overrides? Both abilities are very similar with similar wording in the tooltips.
For a while there was a robot encounter in Maelstrom Prison that would ignore my trooper's Hold The Line ability but that was promptly fixed. Now if they are going to have bosses that are allowed to ignore anti-physics abilities like Hunker Down, entrench, hydraulic overrides and hold the line, the boss should have a BUFF on the bar so that the trooper/smuggler/sniper/BH doesn't bother using the ability expecting it to work when it doesn't!
It should be also noted that those of us who play these classes have experience using these abilities against numerous mobs and bosses - and having that ability work! So we're accustomed to entering the fray expecting to use some of our channeled, hard hitting abilities like Flamethrower against a boss to get some hard, quick damage before being knocked around like a bunch of namby-pambys. Since an AP has the flamethrower buff which makes it uninterruptible (except for knockbacks), we'll use Hydraulic Overrides to remain stationary and get some good DPS on the boss before that ability wears off. Few things are more frustrating than stacking 3 prototype flamethrower buffs, hitting hydraulic overrides and channeling flamethrower ONLY to be knocked back and thus interrupted!
In my opinion, Hydraulic Overrides should either WORK ALL THE TIME, or NOT AT ALL. Or at the very least, give these bosses that IGNORE the ability a special buff or something to let these people know not to burn a useless ability in the encounter.